1. Field of the Invention
The present invention relates to unloaders of the type that include belt conveyors and scrapers disposed at an inlet end thereof and, more particularly, to a belt clamp type unloader capable of continuously conveying and discharging upwardly a bulk material such as a powder, a granular material, a viscous material, or a semi-fluid material.
2. Description of the Related Art
Such continuous type unloaders are widely used in discharging bulk materials such as cereals or fertilizers from the hold of a ship. This type of unloader is typically comprised of a scraper for scraping together the material and a vertical conveyor disposed at a position above the scraper for conveying the material either vertically or diagonally in the upward direction. A typical known type of scraper is constituted by a combination of a paddle feeder having a multiplicity of scraping plates around its periphery and a horizontal screw constituted by a spiral blade, as disclosed, for example, in Japanese Utility Model Unexamined Publication No. 58-114232. In Japanese Patent Unexamined Publication No. 54-100073, for example, a typical known type of vertical conveyor is disclosed which includes a pair of endless belts which are superposed with their respective conveyance faces facing each other, and which pair is vertically disposed; and a plurality of rollers so disposed as to press only the breadthwise sides of the superposed portions into contact with each other, the space between the breadthwise middle portions of the endless belts being allowed to expand freely. Also known is another conventional type of conveyor which employs a bucket elevator or a special belt with a laterally or wave-like ribbed side.
However, if any of the above-described conventional unloaders designed to discharge a grain- or powderlike material is employed to discharge a bulk material having a great degree of adhesivity such as dust coal, earth, sand, or ready-mixed concrete, the material will adhere to the inner surfaces of the buckets or the grooves in the special belts, and this may lead to critical problems hindering normal discharge operations. In the case of the bucket elevator type unloader, if the material to be discharged is continuously spattered up toward the buckets by means of the paddle feeder, the buckets can only retain a limited amount of material, and the spaces between the buckets do not contain any material. Therefore, the efficiency of conveyance is greatly restricted. In the case of the previously-mentioned unloader which includes a pair of superposed endless belts with their middle portions remaining free, it is difficult to positively form a cross-sectional area suitable for conveyance of the relevant material. Therefore, the material is not effectively gathered in the space between the middle portions of the belts; rather, it is scattered around. Otherwise, the material may impose an excessive load on the middle portions of the belts, with the result that the lifetime of the belts is inevitably reduced. Other examples of the related art include a screw type unloader adaptable to the discharge of a material having a great degree of adhesivity, or a pneumatic type unloader for discharging a light-weight grain- or powder-like materials. However, since these types of unloader consume large amounts of energy, it is difficult to apply them to conveyance of materials over long distances. In addition, all of the aforesaid unloaders are disadvantageous in that their mechanisms are complicated and expensive.